Sesbania sesban: widely distributed multipurpose NFT

Sesbania sesban is a many-branched, soft-wooded tree that grows
rapidly and is useful for fodder and green manure. This species has long been
used for browse and soil improvement in India and Africa. Recent interest in
multipurpose, nitrogen fixing trees has caused it to be collected, studied, and
recommended for fodder ''banks" and alley cropping.

Botany

Sesbania sesban (L.) Merrill is a tree that grows to 8 m height.
This papilionaceous (pea-like flowered) legume bears racemes of 4-20 yellow
flowers that may be lightly to heavily streaked with purple. Sesbans have
pinnate leaves with 20-50 opposite pinnules on a rachis 3-12 cm long. The leaf
rachis and the underside of the leaflets are often pubescent. The pods are
usually 10-20 cm long and contain up to 40 seeds that are brown, or dark green
mottled with black. The trees usually have one main stem, but they may develop
many side branches if they have space. Sesban's many branches often give the
tree a shrubby appearance. It tends to have a spreading habit due to its wide
branching angle (as wide as 4560°).

Within its genus, sesban is classified in the subgenus Sesbania,
and thus is more closely related to the annual sesbanias grown far green manure
(such as S. cannabina, others?) than to the - other well known perennial species
of the genus, S. grandiflora, which is in the subgenus Agati (Evans 1990).
Several varieties of sesban are recognized. The botanical distinctions among
sesbanias are often difficult far non-botanists to see, and sometimes sesban is
confused with the annual types of sesbania.

Ecology

Sesban occurs naturally in semiarid to subhumid areas with
5002000 mm of rainfall. It seems to do well under bimodal rainfall
distributions, where heavy rains and even flooded conditions are followed by a
pmgressively drier season. It grows from sea level to 2000 m elevation, but the
upper limit is uncertain. It does not tolerate frost. It is uniquely well
adapted periodic waterlogging and flooding. Soil alkalinity and salinity is
tolerated to a considerable degree. Some research suggests that certain sesban
types may grow well on acidic soils. Sesbans are relatively short-lived, and
under intensive browsing or cutting management will not last more than 3-5
years. Their rapid seedling growth is conducive to short-term fallows and to
replanting if management should reduce growth vigor.

Distribution

Sesban is found throughout the tropical and subtropical parts of
Africa, Asia, and Australia It is not widely distributed in the Americas. Africa
is its center of diversity, and sesban probably originated there; its former
name is S. aegyptiaca. From northeastern Africa, S. sesban var. sesban and its
variants were spread across southern Asia, possibly by man. Within Africa, S.
sesban var. nubica is the type most commonly found, and there arc several
sesbanias closely related to sesban, such as S. goetzei and S. cinerascens
(Gillett 1963).

Sesbania sesban

Uses

Sesban is mostly used as fodder and for soil improvement. its
wood is used only to a lesser extent (Evans and Macklin 1990).

Fodder.

The leaves and tender branches of sesban are high in protein
(20-25% crude protein) and have high digestibility when consumed by ruminants,
such as cattle and goats. Antinutritional factors are suspected to be present in
sesban fodder. Feeding sesbania fodders to monogastric animals (such as
chickens, rabbits, and pigs) is not recommended.

Reports of feeding sesban to ruminants conflict. Trials in
Australia feeding sesban to heifers showed live weight gains, but trials with
young goats in Samoa found a lack of weight gain. Until further research
provides clear guidelines, caution should be used in feeding ruminants with
sesban fodder at more than 10-20 percent of diet.

Soill lmprovement.

Sesban establishes quickly and grows rapidly. In Africa it is
often allowed to grow scattered throughout annual crop fields for the nitrogen
it provides. It has been used in experimental alley cropping systems to provide
mulch and greenleaf manure to intercrops. Sesbans can be somewhat shallow
rooted, and may compete with adjacent crops.

Wood.

Sesban's wood is light in weight compared to the woods of
Calliandra and Leucaena, but it is often harvested for firewood in Africa and
India It has been used in India to make charcoal. The wood is not durable and
should not be considered for timber use. The branches have been used as poles in
temporary structures such as sheds and mud daub huts.

Because sesban grows so rapidly, it has potential for pulpwood
production. Plantings at about 10,000 tree/ha have produced 15-20 tons of woody
biomass (dry weight) in one year.

Food.

Flowers of sesban are known to be added to stews and omelets in
some regions, perhaps mainly as a decorative element.

Other uses.

Various medicinal uses for sesban have been recorded in Africa
and Asia (Evans and Rotar 1987, Evans and Macklin 1990). The leaves and flowers
are used in medicinal poultices and teas. which are said to have the effect of
astringence, or contraction of body tissues. Bark exudates from sesban produce a
gum of medium commercial quality.

Culture and Management

Sesban is generally propagated from seed, although it has been
rooted from cuttings, and research has revealed that it can be established by
tissue culture. Seed scarification usually improves germination. Recommended hot
water scarification is a 30second dip in water heated to just below boiling.
Seed weights range from 55-80 per gram for S. sesban var. sesban to 80-130 per
gram for var. nubica.

Plants grown for fodder production can be placed as close as
30-50 cm apart in rows 1 m apart. Appropriate distances between rows in alley
cropping will depend on the variety grown, the ecology of the site, and
intensity of management.

Experimental fodder cutting trials have yielded 20 tons/ha dry
matter in the first year. However, sesban cannot be managed with the severity
that Leucaena tolerates in fodder and wood biomass production systems. If sesban
is cut too low (below 50-100 cm) or too frequent (more than 4-6 cuttings per
year) death of the plants can result. When cutting sesban it is recommended to
leave 10-25% of the foliage on the plants.

In some climates, such as the highlands of Kenya, sesban may
have a sparse canopy and weed competition can be a problem. This characteristic
makes sesban a good intercrop. Sesban has been grown with the fodder grass
Brachiaria mutica in India, and to provide shade to young coffee plants in Kenya
In climates where sesban grows more vigorously, weeds are shaded out and
companion plants may be adversely affected; this type of growth has been
observed in Hawaii and Jamaica (Roshetko et aL 1991).

Symbiosis

The rhizobia strains that nodulate sesbanias are somewhat
specialized and may not be present where sesbanias have not been grown
previously. Test plantings should be done to see if effective rhizobia are
present in the soil. If not, use of a rhizobia inoculant at planting will be
necessary.

Limitations

Sesban is not a tree for timber or reforestation in the ordinary
sense of forestry or silviculture. Because the range of its ecological
adaptability is not yet well known, test plantings should be done before
large-scale plantings are planned. Sesban has been observed occasionally to die
back under cutting management; fungal infection may be the cause. Leaf-feeding
insects sometimes limit production. Seed chalcids can reduce seed recovery.